1. Field of the Invention
This invention relates to computer peripherals, and more particularly to a self-locking hub for a computer tape drive.
2. Related Art
Magnetic tape drives have long been used for storage and retrieval of information, particularly in connection with high speed digital computers. A tape supply reel is normally secured on a supply hub and the free end of the tape is threaded along a predetermined path past a read/write head assembly. The tape end is then secured to a take-up reel mounted on a take-up hub. The supply and take-up hubs have individual drive motors. In response to various commands sent to the magnetic tape drive, the reels are simultaneously rotated clockwise or counter-clockwise so that various blocks of data on the tape may be read or written by the head assembly. However, the drive motor of the reel from which tape is unwinding at any one time is operated to provide torque in the appropriate direction to maintain approximately constant tension on the tape. Thus, the drive motor may provide torque in either direction with respect to the direction of tape motion. Such torque helps to maintain the tension of the tape across the read/write head assembly, and to prevent tape spillage upon a reversal of direction.
Standardized 9-track tape reels are designed for a friction drive hub. In order to prevent slippage of a tape reel around a drive hub, and to prevent a tape reel from falling off of a drive hub, each reel must be clamped to its respective hub so that a positive drive is established for precisely controlling the rotation of the reels during the normal read-write operation of the tape drive. In the past, this has been accomplished by manually securing reels to tape hubs by means of mechanical clamping mechanisms.
In recent years, the advent of horizontal-mount open reel tape drives has permitted a design in which the hubs are not directly exposed. A user inserts a tape into a slot, and a mechanism centers the inserted tape reel on a drive hub, automatically clamps the tape drive to the drive hub, and automatically threads the tape past the read/write head assembly and attaches the tape to the take-up reel. Two such designs are shown in U.S. Pat. Nos. 4,236,682 and 4,243,186.
It would be desirable to automatically secure or lock a tape reel to a drive hub without manual intervention. In the past, automatic hub locking mechanisms have typically relied upon one of two approaches: (1) use of a separate motor or actuator to directly clamp a reel to a hub, by means, for example, of an expansion ring, or (2) use of a solenoidtype mechanism to hold a hub in place and permit the torque of the drive hub motor to actuate a locking mechanism. An example of one such mechanism in the first category is shown in U.S. Pat. No. 4,236,682. An example of one such mechanism in the second category is shown in U.S. Pat. No. 4,243,186.
A problem of such automatic reel locking devices is that they are very complex, requiring not only electro-mechanically sophisticated apparatus, but also special sensing and/or control mechanisms to properly engage the locking apparatus at the appropriate time.
Therefore, it would be desirable to provide a self-locking tape drive hub mechanism that is mechanically simple, requires no special actuators or control systems, is inexpensive to manufacture, and provides automatic self-locking of a tape reel to a drive hub.
The present invention accomplishes these goals.